Time and again, when discussing connectors and karabiners, I will harp on about how I think that rings are such fantastic connecting elements, providing a uniform breaking strain, without locking mechanisms which could be cross loaded – and just generally wonderful.
When considering hardware on rope bridges of harnesses there are further factors that come into play, such as the fact that the ring is free to rotate.
This means that wear is spread evenly all around the ring, at least in theory. Every so often, however, there will be a ring that has two grooves, one opposite the other. This is probably due to very slight unevennesses in the surface, that cause the rope to locate in that area, once an indentation is started, this will alternate between rope bridge and connector, this is the reason for the grooves being directly opposite each other.
Having said this though, the kind of wear described above is relatively rare and the fact remains that wear on rings is reduced due to the way that they are able to rotate freely und thus spread the load and the wear over a large area.
In the image below you can see the very beginning of such damage, where the anodizing is starting to be polished away. This is different from a uniform wear of the anodization, which is normal. In this case you could already feel a slight indentation.
The DMM anchor rings are machined from 7075 T6 aluminum, wich is the highest grade, hardest aluminum available, even so, this kind of damage can occur.
I still remain slightly perplexed by this, in theory I understand the explanation, but one time I came across a ring with wear in three spots, evenly spaced around the inside face. How does that happen? I am not quite sure…
We have done some testing on rings with substantial loss of material and found that the breaking strain was hardly reduced, despite the fact that quite a bit of material was missing, but do not get me wrong: When a groove is detectable, it is necessary to replace the ring.
This matter is exacerbated further when using hardware on the rope bridge with a positive load orientation, such as swivels or rigging plates. In these cases, there is a limited number of positions into which the line can orientate itself, which leads to a much more rapid wear of the element.
The swivel in the images below was in use for six months.
A lot of these swivels are made from a softer aluminum on top of it, to make matters worse. But even DMM’s Axis swivels (not the swivel in the images above), which like the anchor rings are made from 7075 aluminum, will show wear relatively quickly.
Obviously, it would be foolish to over-simplify this matter, there are also other factors in play, such a the weight of the climber, the type of climbing he or she does, the sort of surroundings the harness is being used in, environments with lots of sand or dirt will obviously cause more rapid wear.
In the end it all boils down to the necessity to inspect Personal Protective Equipment on a regular basis, to catch wear before it becomes a problem and to replace it. If you are unsure about the wear on a piece of equipment, I would suggest to discuss it with the person responsible for work safety in your company, the dealer you bought the equipment from and/ or the manufacturer.